Hematopoietic cell transplant (HCT) has been reported to have purged the reservoir of latently HIV-infected cells in one patient who received an HIV-resistant graft. For this approach to become broadly feasible, it is imperative that we determine the factors involved in HCT that contribute to eradication of the reservoir. Project 1 aims to determine what components of HCT are critical for elimination of the latent viral reservoir. The broad aim of Project 1 is to develop a platform for delivery of HIV-resistant cells to replace latently infected cells. In order to accomplish this broad goal, it is imperative that we determine the role of the separate mechanisms that may contribute to long-term elimination of the reservoir: 1) intensive chemo/radiotherapy which may eradicate recipient lymphocytes and dendritic or antigen presenting cells; and 2) reconstitution of immunity with HIV-uninfected and HIV-resistant cells. We hypothesize that both dose-intensity and graft source contribute separately to elimination of latently infected cells. In Specific Aim 1, we will investigate in human subjects both 1) the dose-intensity of conditioning that produces a meaningful reduction in the quantity of latent viral infection, and 2) the role of the graft source in eliminating latently infected cells. In Specific Aim 2, the effect of a lymphoablative conditioning on latently SHIV infection will be studied carefully in a macaque model, so as to separate the role of conditioning from the role of the graft source. Finally, we hypothesize that, in the absence of HIV-resistant cells, the latent reservoir ultimately will be replenished over time by low level replication of virus. In Specific Aim 3, we will investigate the source of HIV responsible for replenishing the latent reservoir, by a phylogenetic analysis of viral sequences obtained from blood, cerebral spinal fluid, and the intestinal tract, before and after HCT. Result from Project 1 will be used together with that from Project 5 to develop a clinical protocol for delivery of genetically modified HIV resistant cells. Project 1 will rely heavily on Core A and Core B, for support of the primate experiments. The phylogenetic sequencing and analysis will be performed by Core C.